1. Field of the Invention
This invention relates to an image display method and apparatus and, more particularly, to a method and apparatus that can perform clipping for any three-dimensional region with a simple configuration at a high speed.
2. Description of the Related Art
Various techniques have been used for two-dimensional clipping to date. Because three-dimensional data has generally been used for CAD (computer-aided design) and CG (computer graphics) in recent years, clipping for three-dimensional regions has been important to eliminate unnecessary data and image processing. Several techniques have been developed for three-dimensional clipping. However, it is difficult to implement these techniques with hardware and to perform them at a high speed because they cannot realize the processing for each pixel. That is, because recent high-speed three-dimensional image display units have high-speed hardware to convert polygons into data for each pixel, a technique is needed to simultaneously perform the clipping for the three-dimensional region on such hardware. However, the prior art techniques do not meet the above requirements. For example, there is a technique called the Cyrus-Beck algorithm for clipping to any convex three-dimensional region. The Cyrus-Beck algorithm clips line segments using the inward normal line on the boundary surface of the region. To execute clipping with the technique when a polygon is developed into pixels, it is necessary to calculate the inner product by referencing every inward normal line on the boundary surface for each pixel. However, this is too complex a calculation for each pixel to implement with hardware.
For details of the Cyrus-Beck algorithm and other techniques, see, for example, the chapter on clipping in "Procedural Elements For Computer Graphics" by David F. Rogers, published by the McGraw-Hill Book Company in 1985.
An object of this invention is to provide an image display method and apparatus that provide three-dimensional clipping at a high speed by simple processing for each pixel and are capable of generating images.